1. Field of the Invention
The invention relates to a process and a device for modifying the temperature of the inking unit of a web-fed rotary printing machine in the event of stoppage of the machine. At least one ink transport roller, in particular, at least one ink distributor cylinder, has a temperature-modifying medium flowing through it in a fashion that can modify temperature. The invention can be used, for example, in rotary printing machines for offset or relief printing. Sheet-fed as well as web-fed rotary printing machines can be used.
2. Discussion of the Prior Art
During printing, heat develops in the inking units of rotary printing machines. The heat develops due to the flexing work of the rubber-covered ink transport rollers, e.g., the ink transfer rollers, the ink application rollers and the rider rollers. Heat is also released due to mechanical stress on the printing ink, e.g., during ink distribution and ink splitting. In fast rotary printing machines, greater heat develops. For this reason, inking unit temperature modification devices have already been proposed, such as that disclosed in U.S. Pat. No. 5,189,960. According to that reference, at least one inking roller is internally cooled during the printing operation. In practice, the ink distributor cylinders are advantageously used for this purpose.
A procedure of this type has the disadvantage that the cooling device loses effectiveness when the inking unit is shut down, e.g., during a machine stoppage. In this state, the lack of ink flow and the fact that the ink rollers do not roll on the cooled distributor cylinder cause the cooling of the ink rollers to be largely interrupted. As a result, the temperature profile established during machine operation in the rubber of the rubber-covered ink rollers levels out. Whereas during continuous printing the maximum temperature is located in the interior of the rubber layer, during a machine stop the temperature profile levels out, i.e., the rubber surface becomes much warmer than under operating conditions. Printing inks must be optimized for these high temperatures. The tack of the ink nonetheless changes during such machine stops, because a great deal of solvent evaporates from the ink on the ink rollers, which are heating up. When the machine is started up again after a machine stop, there is the danger of web breaks due to the adhesiveness of the ink that accompanies its initially increased tack, which causes the web to stick, e.g., on the transfer cylinder. In extreme cases, the ink completely loses its splitting ability. Finally, the change in tack leads to start-up spoilage.
Accordingly, it is an object of the present invention to provide a process and a device for modifying inking unit temperature during a machine stop.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a process for modifying the temperature of an inking unit of a rotary printing machine, which inking unit includes at least one ink transport roller, and rubber-covered ink transfer rollers. The process includes the steps of passing a temperature modifying medium through the at least one ink transport roller, and driving the inking unit during stoppage of the printing machine with the rubber-covered ink transport rollers in contact with the at least one temperature modifying ink transport roller.
Another aspect of the invention resides in a device for modifying the temperature of ink carrying units of a rotary printing machine, which device includes at least one ink transport roller through which a temperature modifying medium flows, rubber-covered ink transport rollers, and at least one motor operatively arranged to drive the inking units during stoppage of the printing machine with the rubber-covered ink transport rollers in contact with the at least temperature-modified transport roller.
Because the inking unit continues to run during a machine stop, effective cooling continues to be provided for the rubber-covered ink transport rollers, thanks to the rolling contact of the latter with the cooled ink transport rollers. An increase in the surface temperature of the rubber-coated rollers is thus avoided. This makes it possible to optimize the printing ink based on the temperature level during continuous printing. Inks that are optimized for continuous printing have improved drying properties. Furthermore, during machine stops, the tack of the ink changes to a lesser extent than before, so that start-up spoilage and the danger of web breaks is reduced.
The reasons for machine stoppage can be many e.g., in the event of web breaks or other malfunctions or for production changes.
In another embodiment of the inventive process the supply of ink to the inking unit is interrupted during stoppage of the machine.
In yet another embodiment the inking unit is driven at a speed below a maximum possible printing speed. The inking unit can also be driven at a speed approximately between a washing speed and a drawing-in speed.
In another embodiment of the inventive device, a cylinder is provided that prints on printing stock. The inking unit is in a separable drive connection with the cylinder. The at least one motor is arranged so as to drive the inking unit when it is separated from the cylinder in terms of drive.
In still another embodiment of the device, two printing groups for printing on a web are provided. Each of the printing groups has an inking unit, and means are provided for placing the inking units into drive connection so as to be driven by the motor.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.